1. Field of the Invention
The present invention relates to biosensors for the determination of a biochemical compound contained in a liquid sample, and more specifically to a channel structure in which a biosensor is located for determining a compound contained in a liquid sample flowing through the channel.
2. Description of the Related Art
The method generally employed in the measurement of biochemical components of a liquid sample such as blood and body fluid involves passing the liquid sample through a narrow passageway to bring it into contact with a biosensor provided in the passageway. The sensor of this type essentially comprises a permeable membrane, an immobilized enzyme and a working electrode. As the liquid flows in the channel, it diffuses through the permeable membrane to the immobilized enzyme. A reaction between the enzyme and a species being analyzed causes a current to flow through the working electrode on which a measurement is made. The amount of the species that can be detected depends largely on its concentration in the vicinity of the membrane. If the liquid sample is too viscous, a smooth flow is impeded, causing the substrate concentration to fluctuate violently.
In order to ensure a smooth sample flow in the channel, the prior art utilized the hydrophobic characteristic of fluorocarbon resin by coating the inner walls of the channel with a thin layer of the resin. However, a small amount of the liquid sample still reacts with the fluorocarbon resin and adheres to the channel walls to eventually form a rugged surface. As a result, measurement was severely affected and reading became unstable.
It is therefore an object of the present invention to provide a measuring apparatus having a channel structure which maintains its passageway under impurity-free condition for an extended period of time to ensure smooth flow of liquid sample being analyzed by a biosensor located inside of the passageway.
According to the present invention, there is provided a measuring apparatus comprising a channel structure having an inlet port and an outlet port and a passageway between the inlet and outlet ports for passing a liquid sample therethrough, the passageway having inside thereof lined with a layer of hydrophilic material. A biosensor located in the passageway detects a biochemical compound contained in the liquid sample. Preferably, the hydrophilic material comprises a metal oxide having a photocatalytic characteristic, which is illuminated with ultraviolet rays. Specifically, the channel structure is formed by a first member having a channel between the inlet port and the outlet port with the inside of the channel being lined with a layer of the metal oxide, and a second member secured to the first member for enclosing the channel, the second member being coated with a layer of the metal oxide so that the metal oxide layer forms a ceiling portion of the enclosed channel.